1. Field of the Invention
The present invention relates, in general, to light emission diode packages with reflective plates of metal and, more particularly, to a light emission diode package provided with a reflective plate of metal for accomplishing an improved heat dissipation effect, in addition to easily controlling its luminance and angular distribution of the luminance.
2. Description of the Prior Art
As well known to those skilled in the art, light emission diode packages (herein below, referred to simply as xe2x80x9cLED packagesxe2x80x9d) are semiconductor devices, which have LED chips acting as light sources and produced by changing the physical and chemical characteristics of some compound semiconductor materials, such as GaAs, AlGaAs, GaN, InGaN and AlGaInP, and radiate colored lights from the LED chips when electrically activated.
The characteristics of such LED packages are typically determined in accordance with colors of emitted lights, luminance, and a viewing angle thereof. Such characteristics of LED packages are primarily determined by the physical and chemical characteristics of compound semiconductor materials of LED chips, and secondarily determined by their package structures for seating the LED chips therein. In the prior art, the improvement in the characteristics of LED packages accomplished by the development of compound semiconductor materials of LED chips is undesirably limited. Therefore, improved structures of LED packages have been actively studied in recent years, in addition to study of the semiconductor materials of LED chips, in an effort to meet the requirement of a high luminous intensity and a desired viewing angle (it may also be referred to an angular distribution of the luminance). That is, while designing LED packages in recent years, it is desired to consider the compound semiconductor materials of LED chips as a primary design factor, and the structures of LED packages as a secondary design factor.
Particularly, both the luminance and an angular distribution of the luminance of LED packages are mainly affected by the secondary design factor, that is, the structures of the LED packages.
For example, a conventional lamp type LED package of FIG. 1a and a conventional surface mounted type LED package of FIG. 1b are compared with each other in their package structures as follows: In the case of the conventional lamp type LED package 10 of FIG. 1a with two leads 3a and 3b, the second lead 3b is provided at its top with a metal electrode surface, which is depressed to form a depression with inclined side surfaces having a predetermined inclination angle. An LED chip 5 is seated in the depression of the metal electrode surface. The two leads 3a and 3b with the LED chip 5 are packaged by a hemispherical casing 7 of transparent mold resin, thus producing a lamp type LED package 10. The conventional surface mounted type LED package 20 of FIG. 1b consists of a molded package body 11 of epoxy resin, and an LED chip 15 mounted on the surface of the body 11 at a chip mounting area. The LED chip 15 is connected to an electrode (not shown) through a plurality of wires 13.
In the conventional lamp type LED package 10, the hemispherical casing 7 acts as a lens capable of controlling the angular distribution of luminance. Particularly, the hemispherical casing 7 controls the angular distribution of luminance in a way such that the distribution becomes narrow, thus increasing the luminous intensity at a predetermined angle. In addition, the light radiated from the LED chip 5 is reflected by the metal electrode surface of the second lead 3b, thus increasing the luminous intensity of the LED chip 5. In comparison with such a lamp type LED package 10, the surface mounted type LED package 20 has a wider angular distribution of luminance and a lower luminous intensity. It is thus noted that the package structures affect the luminance and the angular distribution of the luminance of LED packages. Therefore, in an effort to accomplish desired characteristics of LED packages, there has been proposed a surface mounted type LED package, with an additional light reflecting surface formed by coating metal on an inclined side surface of the chip mounting area of a molded package body and having a predetermined reflective angle.
Different from such LED packages having molded resin bodies, it is almost impossible to desirably control the luminance or the angular distribution of luminance of another type LED package, having a ceramic body consisting of laminated ceramic substrates and widely used in recent years. That is, the chip mounting area of such a ceramic body must be formed through a punching process, a laminating process, and a cutting process, different from the molded resin bodies having chip mounting areas formed through an resin injection molding process. It is thus very difficult to form a side surface of the chip mounting area of the ceramic body in such a way that the side surface has a desired reflective angle.
FIG. 2 is a sectional view of a conventional LED package having such a ceramic body. As shown in the drawing, the ceramic body of the LED package 30 consists of two ceramic substrates 21 and 22, each of which is formed by laminating a plurality of ceramic sheets. Of the two ceramic substrates 21 and 22, the lower substrate 21 is provided at its top surface with a chip mounting area for seating an LED chip 25 thereon. An electrode 23 extends outward from the edge of the chip mounting area to the lower surface of the lower ceramic substrate 21 to cover a part of the lower surface after passing over the side surfaces of the lower ceramic substrate 21. The LED chip 25 is electrically connected to the electrode 23 using a plurality of wires 27 through a wire bonding process. The upper ceramic substrate 22 is bonded to the top surface of the lower ceramic substrate 21, and forms a predetermined cavity surrounding the chip mounting area.
The cavity surrounding the chip mounting area of the ceramic body is formed through a punching process or a cutting process, so the inside surface of the ceramic body defining the cavity is formed as a vertical surface. Therefore, different from the LED packages having the molded resin bodies, it is difficult to form a coated metal layer on the vertical inside surface of the ceramic body. An additional inclined surface made of resin may be formed on the vertical inside surface of the ceramic body, with a metal layer coated on the inclined resin surface in an effort to overcome the above-mentioned problems. However, the inclined resin surface may be easily deformed, so it is almost impossible to form a desired reflecting surface on the ceramic body.
In the conventional LED packages having such ceramic bodies, it is only possible to control the luminance and the angular distribution of the luminance by changing the dimension of the chip mounting area and/or the thickness of the upper ceramic substrate determining the height of the cavity. Therefore, it is difficult to produce LED packages having ceramic bodies and meeting the requirement of a high luminous intensity and a desired angular distribution of luminance. However, the ceramic substrates of such LED packages have high heat conductivity and a high heat dissipation effect, thus effectively solving the problems of thermal degradation of LED packages and thermal stress of package bodies caused by heat radiated from LED chips. Therefore, it is desired to propose more effective LED packages, which use such ceramic substrates having a high heat conductivity and a high heat dissipation effect, and overcome the structural faults experienced in the conventional LED packages with ceramic bodies due to the vertical inside surface of the ceramic body and leading to difficulty in the control of luminance and angular distribution of the luminance of the LED packages.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an LED package, which has a ceramic body consisting of laminated ceramic substrates, with a reflective plate made of a thin metal sheet and attached on the vertical inside surface of the ceramic body defining the cavity of a chip mounting area, and which thus accomplishes an improved heat dissipation effect thereof, in addition to easily controlling its luminance and angular distribution of its luminance.
In order to accomplish the above objects, the present invention provides an LED package, comprising: a first ceramic substrate having a chip mounting area on a top surface thereof, and provided with a predetermined conductive pattern formed around the chip mounting area; at least one LED chip seated on the chip mounting area of the first ceramic substrate, and connected to the conductive pattern; a second ceramic substrate mounted on the first ceramic substrate and having a cavity at a position corresponding to the chip mounting area; and a reflective plate made of metal and provided in the cavity of the second ceramic substrate so as to surround the LED chip.
In the LED package, the reflective plate preferably has a cylindrical structure, with a diameter of the upper end thereof being larger than that of the lower end thereof.
In such a case, the reflective plate can control the angular distribution of luminance of the LED chip by changing the angle of inclination of the sidewall of the reflective plate, with the inclination of the sidewall being formed by a difference in the diameter between the upper and lower ends of the reflective plate. In addition, the reflective plate can control the luminance of the LED chip by changing the surface area surrounding the LED chip. Furthermore, the reflective plate can control the luminance of the LED chip by selecting a reflective plate made of metals with different reflectivities. Therefore, the present invention provides a variety of LED packages, which are produced using ceramic substrates and have the luminance and angular distribution of the luminance both being controlled as required by users.
In the LED package of this invention, the reflective plate is preferably mounted to the upper surface of the second ceramic substrate around the upper edge of the cavity, thus effectively dissipating heat to the outside of the LED package. In order to allow the reflective plate to effectively dissipate heat to the outside of the package, the mounting of the reflective plate to the upper surface of the second ceramic substrate is preferably accomplished by a silicone-based bonding agent having high heat conductivity.
In order to enhance the heat dissipation effect of the LED package, the LED chip is airtightly packaged by a molded insulating part, which is made of a transparent moldable material and connected to the reflective plate. In such a case, heat dissipated from the LED chip is effectively transferred to the reflective plate having such high heat conductivity. In the present invention, the transparent moldable material of the molded insulating part is selected from epoxy resin or silicone-based resin. Of course, it is possible to use another resin of high heat conductivity as the transparent moldable material of the molded insulating part.
It is more preferable to extend the upper edge of the reflective plate to a predetermined position on the upper surface of the second ceramic substrate, in an effort to more effectively dissipate heat from the reflective plate.
In another embodiment of this invention, the LED package has a hemispherical lens covering the top of the cavity of the second ceramic substrate. In such a case, it is possible to control the angular distribution of luminance of the LED chip by controlling the distribution of curvature of the lens. The hemispherical lens is preferably made of a polymeric material.
In the present invention, the first ceramic substrate preferably consists of a ceramic substrate part having a heat dissipating hole formed therethrough, and a ceramic sheet covering the heat dissipating hole at the upper surface of the ceramic substrate part. In such a case, both the chip mounting area and the conductive pattern are formed on the upper surface of the ceramic sheet. The heat dissipating hole of the ceramic substrate part is filled with metal paste.